Intelligence, Surveillance, and Reconnaissance (ISR) is a practice that assists a force in employing sensors to gather data, then managing or processing that data to produce information. ISR is most commonly employed by military forces, and is often leveraged to improve a commander's situational awareness and consequently their decision making. Apparatus and methods for ISR are essential to such processes. And object of ISR is often to detect, identify, or track a target.
Imaging sensors for ISR in the prior art tend to use focusing elements to direct electromagnetic radiation coming from a target of observation onto an image sensor located at or near the device's focal plane. Some prior art systems exist which use radiation across a wide range of the electromagnetic spectrum, from microwave radio (radar) up through infra-red and visible light (electro-optical and infrared, or EO-IR).
Some gimbaled prior art systems for ISR exist that can be mounted on an aerial platform and can carry multiple sensors on the same gimbal. These prior art systems tend to be either only daylight capable or are electro-optical and infrared.
Prior art systems can be categorized by the source of the electromagnetic radiation used to detect a target, selected from a list consisting of: natural illumination, self-illumination, and artificial illumination.
Natural illumination systems use sun-light, moon-light, star-light, or man-made radiation sources not resulting from any action of a remote observing platform to illuminate a target object. Natural illumination typically carries significant energy in the visible part of the spectrum, with electromagnetic wavelengths between 0.390 and 0.750 micrometers.
Unless the context dictates the contrary, all ranges set forth herein should be interpreted as being inclusive of their endpoints and open-ended ranges should be interpreted to include only commercially practical values. Similarly, all lists of values should be considered as inclusive of intermediate values unless the context indicates the contrary.
The blackbody radiation emitted by objects at or near room temperature is often sufficiently intense to be detected by an ISR system; such systems are referred to as self-illumination systems. Self-illumination results in radiation predominantly in the infrared region of the spectrum, with wavelengths in the range of 3-5 micrometers. Self-illumination of room-temperature objects produces such small amounts of energy in the visible and shorter wavelengths as to be unobservable by practical sensors.
Artificial illumination systems comprise components that generate illuminating radiation and direct this illumination at a target for the purpose of reflecting radiation to generate an image on a sensor or receptor. Common examples of artificial illumination systems include ordinary flash camera which fires the flash bulb to illuminate a target object in the resulting photograph captured by the camera sensor. Artificial illumination is generally considered undesirable in ISR applications because the illuminating energy radiated from the ISR apparatus can be detected.
A relevant physical law for remote optical systems is known as the diffraction limit of resolution. The angular resolution of an imaging device is defined by the size of detail that can be distinguished by the device. Fundamental physics involving the diffraction of electromagnetic radiation puts limits the angular resolution that can be achieved, and can be expressed by the equation:sin(θ)=1.220 λ/D where θ represents the angular resolution in radians, λ represents the wavelength of the radiation in meters, and D represents the diameter of the sensors receiving aperture in meters. This relationship limits the practical usage of prior art ISR systems, forcing systems which require high resolution for target identification to operate close to the target. Such prior art systems may also have to operate in the daytime in order to capitalize on the present natural illumination.
It is well known that natural solar illumination contains significant energy content in wavelengths spanning from approximately 0.1 micrometers to 10 micrometers. Wavelengths greater 0.390 micrometers comprise the visible and infrared spectra, and are used extensively by a variety of prior art ISR sensors, but these sensors suffer from the wavelength-based fundamental limits on angular resolution imposed by the diffraction limit of resolution.
Thus, in ISR applications there is a need to detect, observe, identify, confirm, and track targets, in all conditions, both day and night, often from remote and aerial platforms. Further, there is a need for such systems to have a low probability of detection, to be compact and portable by aerial platforms, to function from great distances, to use methods enabling both target detection and target identification with minimal operator interaction. This combination of needs has not been met by the known prior art.